Software Defined Radio (SDR), a radio that provides software control of a variety of modulation techniques over a broad frequency range, is an emerging technology that offers numerous advantages over conventional radio designs. With SDR, one would implement a common hardware platform and accommodate the different communications standards and technologies via software modules and firmware. This platform must be compatible with the high degree of versatility of SDR-based communication systems. SDR technology is being promoted by the US Department of Defence to replace tens of thousands of single protocol, single use radios with a common platform that could be reprogrammed to ensure interoperability. Military and public safety organisations from around the world are also considering this technology to solve their interoperability problems.
Although SDR can be easily implemented below 6 GHz using conventional electronics, it is increasingly difficult to do so at the higher operating frequencies proposed by many new wireless and SATCOM standards. To take full advantage of the SDR concept, a hardware platform is required that is capable of continuous operation from frequencies where electrical sources have difficulty providing continuously tunable operation, up to 60 GHz. In addition, various signal modulation schemes will need to be supported.
We present here a prototype for such a transmitter based on optical technology. It can generate a RF carrier tunable from about 18 to more than 40 GHz, which can be modulated using both intensity and phase modulation techniques. Simulations and experimental results are presented.